problems with recording "digital noise"

synthesist

hey!

I got a problem with recording diy gear with my computer.

I build a kind of ringmodulation using a cd4046 chip. I can also creat a digital noise when I play my super-psycho-modulation source through it.

But the volume of the record suddenly gets silent half the way. Then it gets loud again - and then silent. Only with this module though!

I thouht like there is some AC-bleed through or something, but the signal goes through a filter - then a VCA and then a mixer before the computer gets it.

Any idea?

synthesist · Posted: Thu Apr 26, 2012 4:29 am Post subject:

o.k. so I tried to play my gear through a DJ-Mixer before the signal passes the computer. Unlike what I said first - now I got the same problem with every module Crying or Very sad

Such a mess! I only know this problem from back in the days when I tried to record a CMOS oscillator right throuh the Computer.

Do you guys think it could be soundcard?

elektro80 · Posted: Thu Apr 26, 2012 4:55 am Post subject:

You could possibly check if something changes if you use a DI box.
Lunetta/digital noisebox thingie -> DI and then to mixer/filter /recording device or what have you..

Read this: http://www.soundonsound.com/sos/jun02/articles/diboxes.asp

elektro80 · Posted: Thu Apr 26, 2012 5:12 am Post subject:

BTW.. it is also probably smart to make sure that you have a low cut and a high cut filter.. rather steep.. before the DI. It makes good sense to kill those parts of the signal that are outside of the bandwidth you want to record.
That being said, if this is "digital noise" at audio rate.. then I would consider moving the high cutoff freq from say 15-18khz down to say 4-8khz and see if that changes anything. As for the low cutoff.. it all depends on how steep your filter is.. and the signal.. but IMO your "digital noise" should be clipped at 50-200 HZ. A filter has a rolloff per octave.. so you must experiment a bit until you get it right.

inlifeindeath · Joined: Apr 02, 2010 Posts: 285 Location: Albuquerque, NM

did you try an opamp or transistor buffer before going into the sound card?

synthesist · Posted: Thu Apr 26, 2012 12:54 pm Post subject:

thanks for the help,

elektro 80: there is always some high tones bleeding through the audio even if I cut off everything with my ms20 filter clone, also the analog vcos bleed throuh. A DI Box should help there I guess. But I dont wanna buy one if I dont know it helps. Just bought a new Midi to CV interface...

But I remember I could record whole sessions without problems formerly Confused

I would just say it is the soundcard, but also I am sure it makes a difference what device I record. so Confused

inlifeindeath: my diy - mixer uses an opamp. and after it, the signal goes to the dj-mixer and then it passes the computer.

elektro80 · Posted: Thu Apr 26, 2012 1:33 pm Post subject:

I had some amusing moments with my first PPG Wave 2.2 when I figured out that it bleed HF shit into the audio outs.. and it would even mess with the tape bias. Hilarious! Very Happy

elektro80 · Posted: Thu Apr 26, 2012 2:32 pm Post subject:

Try to find some scope/spectral analysis software for your computer and use it to figure out what the signal looks that hits the sound card.

It is possible to build a very simple and inexpensive transformer based DI yourself. However, in this particular case it would be smart to follow my advice and apply some low cut and high cut on the signal before it goes to the DI.